Automotive vehicles increasingly incorporate inflatable restraint devices for protecting occupants during crash and rollover events. These airbag devices may be located in the instrument panel or steering wheel for frontal impacts, or in the interior sides or roof of the vehicle for side impacts or vehicle rollover.
Although offering the potential to save lives or reduce the seriousness of injury, these devices can also present a danger of their own. In order to provide effective protection, particularly during crash events, it is necessary to deploy the inflatable devices within a very short time span; typically within 5 to 20 milliseconds. Given the energy involved in a crash event, the deployment of the inflatable devices must also be extremely forceful. If an occupant is not in a proper position, there is potential for bodily harm or death resulting from the deployment of the inflatable device. Other circumstances that can lead to serious injury or death are the presence of a small child, and particularly in the case of a frontal airbag, a child situated in a rear facing child seat.
In order to mitigate the likelihood of injury or death directly resulting from inappropriate airbag deployment, it is necessary for the system controller, prior to airbag deployment, to first determine the presence of an out-of-position occupant, a child occupant, or a child occupant situated in a child seat and, in the latter case, whether the child seat is facing forward or rearward. Based on these factors (and other information), the decision can be made by the controller for either no deployment, full deployment, or, in the case of multiple stage airbags, deployment with reduced energy.
There is a further need for occupant presence and position detection relating to cost savings to the consumer. Once an airbag has deployed, it is not reusable. By inhibiting airbag deployment in the instance where no occupant is present within the envelope of protection offered by the airbag, the considerable cost of removing and replacing the airbag while repairing the vehicle is avoided.
A number of methods of detecting occupant presence and position are either in use or have been proposed. These include the use of ultrasonic, radio frequency or optical sensing means that generate an electronic “image” of any objects within the envelope of protection offered by the airbag. These methods are not without shortcomings. In addition to the considerable computing power required to ascertain the shape and location of the object, the possibility exists that the object can be misinterpreted. For example, an occupant seated in the proper position but reading a newspaper might be interpreted as an inanimate object.
Another approach is to determine the weight of an object located in a seat. This can be accomplished either by measuring the overall weight of the seat with sensors at its attachment point and then calculating the weight of the object or occupant in the seat, or by directly measuring the object or occupant weight by means of a sensor or sensors located within the seat structure. An example of the latter is taught in U.S. Pat. No. 5,975,568 to Speckhart et al. (incorporated herein by reference) that discloses a weight-sensing pad incorporated into an automobile seat. The pad is comprised of a bladder containing a non-compressible fluid in conjunction with a pressure sensor disposed under the foam seat cushion. Weight on the pad increases the sensed pressure value, which can then be used to infer the weight of the occupant.
Sensing the weight alone of an object contained within the seat, although useful information, is nonetheless an incomplete depiction of the information desired for making an airbag deployment decision. The weight parameter alone does not, for example, provide discrimination between animate and inanimate objects. In the case where the object is a human, weight measurement provides minimal, if any, indication of whether the occupant is in the proper position for an airbag deployment.
Other methods are described in the art which employ proximity sensors to detect the presence and location of a vehicle occupant. For example, U.S. Pat. No. 6,158,768 to Steffens et al. discloses an array of capacitive electrodes disposed in and around the automobile seat. The presence and relative position of a vehicle occupant within the electrostatic fields set up by the electrodes is then sensed. The occupant's weight is not measured directly, but rather inferred from a measure of the occupant's girth as measured by the capacitive array.
Yet another approach for detecting occupant presence and position is disclosed in U.S. Pat. No. 6,927,678 to Fultz et al. (incorporated herein by reference) which involves the use of a capacitive array similar to that taught by Steffens et al. in conjunction with a fluid filled bladder, as taught by Speckhart et al. In the Fultz et al. arrangement, the bladder does not employ a sensor means for directly measuring the increase in fluid pressure caused by the presence of an occupant or object in the seat. Rather, a capacitive array is disposed in the seat bottom, with the electrodes capacitively coupled to a reference plane. The fluid filled bladder is disposed between the capacitive electrodes and the reference plane such that, as the weight of the occupant compresses the bladder, the electrodes are urged into closer proximity with the capacitively coupled reference plane. Depending on the amount of change of capacitance and the relative difference of capacitance between the electrodes, various information about the occupant size, location, and weight can be calculated.
Another use for capacitive arrays has been disclosed in U.S. Pat. No. 5,691,693 to Kithil (incorporated herein by reference). In that invention, an array of capacitive sensors is located proximate to the head of a vehicle operator. The signals from the array are fed into a microprocessor which triangulates the head position and tracks head movement in order to discern patterns of movement indicative of operator impairment due to fatigue, alcohol/drug use, etc.
The capacitive electrodes of these and similar systems are typically constructed of copper or aluminum metalization on a flexible substrate. The electrical connection to the metalized areas is typically done by soldering; therefore, the substrate material must be able to withstand high temperatures associated with soldering. Substrate materials, such as polyamide, that are capable of withstanding soldering temperatures are more costly that otherwise suitable substrate materials, such as polyester.
Another significant cost associated with manufacturing traditional capacitive arrays is the materials and processes used to deposit the electrical traces onto the flexible substrate. The typically used photoetching process requires a number of complex process steps before the complete circuit is fabricated. Use of this process also requires compliance to environmental plating regulations, which further adds to its cost. Moreover, it is not unusual for pricing fluctuations of 50% or more for the metals typically used as the conductive material. A lower cost and simpler materials and manufacturing solution would therefore be advantageous.
It is often desirable to dispose arrays in multiple layers on the same substrate. However, the conventional processes of depositing metal conductors on a substrate do not easily lend themselves to this need.